(1) Field of the Invention
The present invention relates to a nuclear magnetic resonance probe (hereinafter referred to as an “NMR probe”) and an NMR spectrometer using the same, and more particularly to an NMR spectrometer which is characterized by a circuit configuration and mounting configuration of a probe antenna for transmitting radio frequency signals at a prescribed resonance frequency to a sample placed in a static magnetic field and/or receiving free induction decay (FID) signals.
(2) Description of the Related Arts
Nuclear magnetic resonance (NMR) spectroscopy, by which one can get atomic level information on matter, is an excellent method of analyzing the structure of a compound. The basic principle of analysis by this method is as follows: a sample placed in a static magnetic field is exposed to a radio frequency magnetic field and a response signal from the excited nuclear spin is received and analyzed. For high resolution analysis, an NMR spectrometer which has a superconducting magnet capable of generating a static magnetic field (B0) is employed. Currently, a 21.6 T (920 MHz) NMR spectrometer is available as an NMR spectrometer which is primarily intended to analyze three-dimensional protein structures.
In protein analysis, the sample volume is very small and the intensity of generated free induction decay (FID) signals is weak. Therefore, a probe for receiving FID signals must be highly sensitive. The reduction in thermal noise upon the detection of signals is effective for enhancing a signal-to-noise ratio (S/N) that is the index of the sensitivity for the NMR spectroscopy. Therefore, a method of cooling a probe to a low temperature has been known, and such probe is referred to as a cryogenic probe. The example of a cryogenic probe is disclosed in the U.S. Pat. No. 5,247,256. The signal intensity depends upon a Q factor (quality factor) of a probe antenna, and an antenna should have high Q factor for realizing high-sensitive NMR spectroscopy. Since the Q factor depends upon the resistive loss of an antenna, examples of effective means for enhancing a Q factor include using a low-resistance conductor for fabrication of a probe antenna, cooling a conductor to reduce resistance, or applying a superconductor, which has resistance much smaller than that of a normal metal, to a conductor of a probe antenna. The example of using a superconducting material to a probe antenna is disclosed in U.S. Pat. No. 5,585,723.